Acid in milk is a term used to describe the presence of certain acids found in milk. Lactic acid, with 6 letters, is an organic acid that is produced by the fermentation of lactose. Amino acid, with 5 letters, is an organic compound that contains both an amino group and a carboxylic acid group. Oleic acid, with 5 letters, is a monounsaturated fatty acid found in many animal and vegetable fats and oils. Boric acid, with 5 letters, is a weak acid that is often used as an antiseptic, insecticide, flame retardant, or neutron absorber. ETCH, with 4 letters, is a process of using an acidic solution to corrode a surface, such as metal, in order to create a design.